Sheet feeding device and image forming apparatus

ABSTRACT

An exemplary embodiment of the invention provides a sheet feeding device in which the vibration and noise can largely be reduced in a rotating shaft of a pressing roller while multi feed is sufficiently prevented. A top-most sheet P stacked on a sheet stacking member is drawn by a feed roller and separated one by one between the feed roller and the separating member, and the sheet is fed toward a first sheet guide member. A pair of conveying rollers conveys the sheet while nipping the sheet, and the conveying rollers draws the sheet from a nip between the pressing roller and the separating member. A projection of a second sheet guide member is projected toward a position below a tangent line, so that a force with which the sheet pushes up the pressing roller is eliminated to suppress generation of vibration and noise in the pressing roller.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding device which separates multi-feeding sheets one by one to feed the sheet to an image forming portion on a downstream side, particularly to a structure in which vibration and noise are prevented when the sheet is drawn from the downstream side after feeding of the sheet is stopped.

2. Description of the Related Art

There is widely used a sheet feeding device, in which the sheet passes between a feed roller and a friction separating member pressure-contacting each other and the sheet is separated one by one and fed to the image forming portion on the downstream side.

Japanese patent Application Laid-Open No. 2004-26403 discloses a sheet feeding device, in which the sheet separated and fed by the feed roller and the friction separating member is conveyed to a pair of conveying rollers of the image forming portion and the sheet is conveyed while nipped between the pair of conveying rollers.

In this case, the feed roller is partially cut out, i.e., the feed roller is formed in a so-called crescent shape, and a pressing roller is provided coaxially with the sheet feeding roller. In this configuration, when the sheet reaches the pair of conveying rollers, the sheet is nipped between the friction separating member and the rotatable pressing roller instead of the feed roller having large friction, which prevent the multi feed of the sheet.

Japanese patent Application Laid-Open No. 7-133033 discloses a sheet feeding device in which the sheet is guided while a course of the sheet fed by the feed roller is largely bent toward the feed roller side (so as to wound around the feed roller). In this case, the friction separating member is fixed to a loosely-journaled lever arm, and a pressing spring applies a force to the lever arm to cause the friction separating member to pressure-contact the feed roller. A vibration insulating spring is attached to the lever arm to prevent vibration (noise generation). The vibration is caused by rattling the lever arm around a rotating shaft in drawing the sheet.

Japanese patent Application Laid-Open No. 5-208747 discloses a sheet feeding device, in which a solenoid is provided to move up and down the lever arm to which the friction separating member is fixed. In this case, when the sheet reaches a conveying roller on the downstream side, the solenoid is started up to release the pressure contact between the feed roller and the friction separating member, which reduces the generation of the vibration (noise). The vibration is generated by resistance when the conveying roller draws the sheet and by the rattle around the lever arm.

Recently, for the purpose of miniaturization of the image forming apparatus and reduction of an installation space, there is proposed a structure in which the sheet is drawn while the course of the sheet is bent at a steep angle toward the feed roller side than ever before (see FIG. 1).

In this case, when the conveying roller on the downstream side pulls the sheet, the feed roller (or pressing roller) is raised by the sheet, and the rotating shaft of the feed roller is pulled toward the conveying roller with a large force. When the sheet is intermittently drawn while frictioned with the friction separating member, a sheet drawing resistance is intermittently changed and thereby a pulling force is also intermittently changed, which vibrate the rotating shaft of the feed roller to easily generate the noise in components (such as the pressing roller). When the nipping force of the sheet between the feed roller and the friction separating member fluctuates by the vibration of the rotating shaft, a fluctuation range of the sheet drawing resistance is increased to further amplify the vibration and noise.

The structure disclosed in Japanese patent Application Laid-Open No. 7-133033 in which the vibration and noise on the friction separating member side is prevented using the vibration insulating spring is not enough for a countermeasure against the vibration and noise on the feed roller side. That is, the rotating shaft of the feed roller is vibrated even if the rattle of the lever arm fixed to the friction separating member is eliminated.

As disclosed in Japanese patent Application Laid-Open No. 5-208747, when the pressure contact between the feed roller and the friction separating member is released, the friction separating member cannot block the multi-feeding sheets, which increases a possibility of the multi feed of the sheet which is in contact with the drawn sheet. Additionally, because the structure is also complicated, the miniaturization of the device cannot be achieved.

The invention provides a sheet feeding device in which the vibration and noise can largely be reduced in the rotating shaft of the feed roller while the friction separating member sufficiently exerts the function of preventing the multi feed.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a sheet feeding device includes a sheet feed member which feeds a sheet; a separating member which separates the sheet between the sheet feed member and the separating member; a first guide member which guides the sheet fed by the sheet feed member while bending the sheet toward a sheet feed member side; a sheet conveying unit which conveys the sheet guided by the first guide member while nipping the sheet; and a second guide member which orientates a course of the sheet toward a sheet conveying unit side, wherein the second guide member contacts a surface on the sheet feed member side of the sheet drawn between the sheet feed member and the separating member, on a tangent line of the sheet feed member at a position where the sheet feed member contacts the separating member, or at a position located on a separating member side in relation to the tangent line.

In the sheet feeding device of the invention, when the sheet fed by the sheet feed member is transferred to the sheet conveying unit, the sheet conveying unit draws the sheet from the nip between the sheet pressing member and the separating member.

At this point, the direction in which the sheet is drawn between the sheet feed member and the separating member is located on the separating member side of the tangent line or on the tangent line of the sheet feed member located at the position where the second guide member pressure-contact the separating member. Therefore, the force in the direction in which the separating member is separated from the sheet feed member is applied to the separating member from the conveyed sheet, and the force of the pressure contact between the separating member and the pressing member is weakened, so that the generation of the vibration can be reduced in the sheet feed member.

Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a configuration of an image forming apparatus according to an embodiment of the invention.

FIG. 2 is a perspective view of a sheet stacking member of a sheet feeding device.

FIG. 3 is an explanatory view of assembly of a feed roller.

FIG. 4 is an explanatory view of assembly of a separating member.

FIG. 5 is an explanatory view of a configuration of a sheet feeding device according to a first embodiment of the invention.

FIG. 6 is an explanatory view of operation of a second sheet guide member of the sheet feeding device.

FIG. 7 is an explanatory view of a sheet feeding device according to a comparative example in which the second sheet guide member is eliminated.

FIG. 8 is an explanatory view of a configuration of a sheet feeding device according to a second embodiment of the invention.

FIG. 9 is an explanatory view of operation of a second sheet guide member of the sheet feeding device.

FIG. 10 is an explanatory view of a configuration of a sheet feeding device according to a third embodiment of the invention.

FIG. 11 is an explanatory view of operation of a second sheet guide member of the sheet feeding device.

DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment of the invention will be described below with reference to the drawings.

As described later, a sheet feeding device of the invention can be mounted on not only an image forming apparatus but also various kinds of sheet processing apparatus and sheet processing apparatus including an image reading apparatus.

An image forming apparatus of the invention can be implemented in not only a monochrome printer but also various applications such as an electrophotographic full-color printer, a copying machine, FAX, and a multifunction peripheral. The image forming apparatus of the invention can be implemented in not only the electrophotographic system but also various printing methods in which images are formed in various sheet materials.

The drawings and descriptions are not presented for general configurations and control of the sheet feeding device and image forming apparatus disclosed in Japanese patent Application Laid-Open Nos. 2004-26403, 7-133033, and 5-208747.

(Image Forming Apparatus)

FIG. 1 is an explanatory view of a configuration of an image forming apparatus according to an embodiment of the invention. An image forming apparatus 14 is an electrophotographic monochrome printer.

As illustrated in FIG. 1, in the image forming apparatus 14, a sheet feeding device 1 is disposed in a lower portion of an apparatus main body.

In the sheet feeding device 1 which is of an example of the sheet feeding device, sheets P stacked on a sheet stacking member 13 are separated one by one by a sheet feed member and a separating member 17 and the sheet P is fed to a direction of a pair of conveying rollers 21. The sheet feed member includes a feed roller 15 and a pressing roller 16.

The feed roller 15 is formed in the so-called crescent roller in which a part of an outer periphery is partially cut out. The feed roller 15 feeds the sheet P by contacting an upper surface of the sheet P stacked on the sheet stacking member 13. The feed roller 15 is rotated by one-rotation control using a driving mechanism (not illustrated), and the cut-out portion is rotated once from a position where the cut-out portion faces the separating member 17, thereby feeding the sheet P.

The separating member 17 separates the sheet P one by one while nipping the sheet P between the separating member 17 and the feed roller 15.

A pad arm 17 b and a pressing spring 18 are of an example of a support mechanism supporting the separating member 17. The pad arm 17 b and pressing spring 18 support the separating member 17 while applying a force to the separating member 17 toward the feed roller 15.

A first sheet guide member 22 which is of an example of the first guide member guides the sheet P while bending a course of the sheet P fed by the feed roller 15 toward the side of the feed roller 15.

A pair of conveying rollers 21 which is of an example of the sheet conveying unit conveys the sheet P while nipping the sheet P guided to the first sheet guide member 22.

A pressing roller 16 which is of an example of the pressing member is provided to pressure-contact the separating member 17 when the cut-out portion of the feed roller 15 faces the separating member 17. When the feed roller 15 stops a sheet feeding operation after rotated once to feed the sheet P, the sheet P is nipped between the pressing roller 16 and the separating member 17, thereby preventing the multi feed of the sheet P. The pressing roller 16 is a rotating body which is driven according to the sheet drawn by the pair of conveying rollers 21 while rotatably supported by a feed roller shaft 101 of the feed roller 15.

A second sheet guide member 23 which is of an example of the second guide member contacts a surface on the side (the side contacted by the pressing roller) of the pressing roller 16 which is of an example of the pressing member side of the sheet P fed by the feed roller 15 and the separating member 17. The second sheet guide member 23 orientates the course of the sheet P toward the side of the pair of conveying rollers 21 which is of an example of the sheet conveying unit side. The second sheet guide member 23 orientates the course of the sheet P toward the pair of conveying rollers 21 on the side of the separating member 17 with respect to a tangent line of the pressing roller 16 at the position (nip portion) where the second sheet guide member 23 pressure-contacts the separating member 17. Therefore, although described in detail, the second sheet guide member 23 eliminates or decreases the nipping direction force applied on the pressing roller 16 in association with the sheet conveyance performed by the pair of conveying rollers 21.

The sheet stacking member 13 which is of an example of a sheet accommodating unit retains the sheets P in the stacked state, and the feed roller 15 draws the top-most sheet P while contacting the top-most sheet P retained by the sheet stacking member 13.

The top-most sheet P stacked on the sheet stacking member 13 is drawn by the feed roller 15, and the sheets P are separated one by one in an abutment portion between the feed roller 15 and the separating member 17. The sheet P fed by the feed roller 15 is guided by the first sheet guide member 22 and transferred to the pair of conveying rollers (registration roller) 21. The pair of conveying rollers 21 includes a conveying roller 19 and a conveying roller 20, and the pair of conveying rollers 21 feeds the sheet P to a transfer nip between a photosensitive drum 2 and a transfer roller 6 in synchronization with a head of a toner image formed in the photosensitive drum 2.

A charging roller 3, an exposing device 7, a development portion 5, the transfer roller 6, and a cleaning portion 27 are disposed around the photosensitive drum 2 in an image forming portion G. The photosensitive drum 2, the charging roller 3, the development portion 5, and the cleaning portion 27 are assembled in a cartridge and drawn toward a near side to be able to be exchanged.

The cleaning portion 27 cleans a surface of the photosensitive drum 2, and the charging roller 3 evenly charges the surface of the photosensitive drum 2. Using the exposing device 7, the charged surface of the photosensitive drum 2 is scanned to write an electrostatic image with a laser beam modulated by an image signal to write an electrostatic image. The development portion 5 causes toner to adhere to the electrostatic image on the photosensitive drum 2 to form a toner image while a development sleeve 4 bears the toner stored in a toner container. A transfer voltage having an opposite polarity to a polarity in which the toner image is charged is applied to the transfer roller 6 to transfer the toner image from the photosensitive drum 2 to the sheet P fed to the transfer nip. The sheet P to which the toner image is transferred is fed to a fixing device 10, and the sheet P is conveyed while nipped in a fixing nip between a pressure roller 9 and a heating device 8, thereby fixing the toner image to the surface of the sheet P. The sheet P to which the toner image is fixed is conveyed while nipped between a discharge roller 11 and a discharge roller 12, and the sheet P is discharged to a discharge tray 26.

(Sheet Feeding Device)

FIG. 2 is a perspective view of a sheet stacking member of the sheet feeding device, FIG. 3 is an explanatory view of assembly of the feed roller, and FIG. 4 is an explanatory view of assembly of the separating member.

As illustrated in FIG. 2, the first sheet guide member 22 constitutes a part of a frame body of the resin-molded sheet feeding device 1. An intermediate-plate support plate 122 is fixed to the sheet stacking member 13, and an intermediate plate 120 is rotatably supported by an intermediate plate shaft 121 supported with an intermediate-plate support plate 122. Pressing springs 123 are disposed between the intermediate plate 120 and the sheet stacking member 13, and the pressing springs 123 upwardly apply a force to the sheet placed on the intermediate plate 120 to cause the sheet to pressure-contact a feed roller shaft unit 40.

A feed roller shaft 101 is rotatably supported by a sidewall of the sheet stacking member 13, and symmetrical intermediate plate cams 106 and 107 are fixed to both end portions of the feed roller shaft 101. The intermediate plate cams 106 and 107 are rotated while being integral with the feed roller shaft 101, and the intermediate plate cams 106 and 107 push down the intermediate plate 120 against the pressing springs 123 to separate the sheet placed on the intermediate plate 120 from the feed roller shaft unit 40. A feed gear 108 is fixed to the outside of the intermediate plate cam 106, and selective rotation is transmitted to the feed gear 108 by a solenoid or a clutch (not illustrated).

The feed roller shaft unit 40 is fixed to the feed roller shaft 101, and a separating member unit 41 is disposed below the feed roller shaft unit 40.

As illustrated in FIG. 3, a feed roller holder 102 is fixed in a substantially central portion of the feed roller shaft 101. The feed roller holder 102 is integrally molded using a resin, an facing interval is widened to detachably attached a feed roller collar 103 by pushing down knobs 102 c provided both side faces of the feed roller holder 102.

The feed roller 15 is made of an elastic material such as EPDM and an elastomer which has a high friction coefficient. The feed roller 15 is assembled by enclosing the outside of the half-round feed roller collar 103. When the feed roller 15 is fixed to the feed roller holder 102, two index bosses 103 a provided in side faces of the feed roller collar 103 engage U-shape grooves 102 a provided in the side faces of the feed roller holder 102. At the same time, pawls 103 b provided in the side faces of the feed roller collar 103 engages holes 102 b made in the side faces of the feed roller holder 102. The feed roller 15 is assembled by pressing a saddle portion 104 a against the feed roller shaft 101.

The pressing force pulls the outside of the feed roller 15 in a circumferential direction to wind the feed roller 15 around the outer periphery of the feed roller collar 103 with no gap.

The pressing rollers 16 are rotatably supported on the sides of a hollow sleeve orientated toward the outside of the feed roller holder 102, and pressing roller regulating portions 102 d prevent drop-off of the pressing rollers 16.

As illustrated in FIG. 4, the separating member 17 is made of a rubber material such as EPDM and elastomer, and the separating member 17 is bonded to a pad arm 17 b. A boss extended from a swing support 17 a is fitted in an arm retaining portion 17 d provided in a pad holder 17 e, which rotatably retains the pad arm 17 b. The pressing spring 18 is disposed between the pad arm 17 b and the pad holder 17 e, and the pressing spring 18 generates an applying force toward an obliquely upward direction such that the separating member 17 pressure-contacts the feed roller 15 or pressing roller 16 of FIG. 3.

(Mechanism for Preventing Multi Feed)

As illustrated in FIG. 1, it is assumed that ∥1 is a friction coefficient between the feed roller 15 and the sheet P, μ3 is a friction coefficient between the two sheets P overlapping each other, and μ2 is a friction coefficient between the sheet P and the separating member 17. The friction coefficient μ1 of the feed roller 15 and the friction coefficient μ2 of the separating member 17 are set such that a relationship of an expression (1) is satisfied.

μ1>μ2>μ3   (1)

When a torque is imparted to the feed roller 15, the top-most sheet P1 is fed by a frictional force of the feed roller 15. It is assumed that N is a pressurizing force of the pressing spring 18 and a positive force is applied to the sheet conveying direction, when the sheet P is conveyed to the separating member 17. At this point, a conveying force F1 of the feed roller 15, a drag F2 which the separating member 10 imparted to a sheet P1, and a force F applied to the sheet P1 are computed as follows.

F1=μ1*N   (2)

F2=−μ2*N   (3)

F=F1+F2=(μ1−μ2)N   (4)

As described above, because of μ1>μ2, F>0 is obtained, and the sheet P is fed onto the downstream side according to the rotation of the feed roller 15.

Then, it is considered that the two sheets P are simultaneously conveyed (multi feed). A force FS1 applied to the first sheet P1 is computed as follows.

FS1=F1+F3=μ1*N−μ3*N=(μ1−μ3)N   (5)

where F1 is the conveying force receiving from the feed roller 15 and F3 is a drag receiving from the second sheet P.

As described above, because of μ1>μ3, FS1>0 is obtained, and the first sheet P1 is fed onto the downstream side according to the rotation of the feed roller 15.

On the other hand, assuming that F4 is a conveying force receiving from the first sheet P1, F2 is the drag receiving from the separating member 17, so that a force FS2 applied to the second sheet P2 can be computed as follows.

FS2=F4+F2=μ3*N31 μ2*N=(μ3−μ2)N   (6)

As described above, because of μ2>μ3, FS2<0 is obtained, and the second sheet P2 is blocked by the separating member 17. Even if the pressing roller 16 nips the sheet P, the multi feed of the second sheet P2 is continuously blocked because the pressurizing force N of the pressing spring 18 is not changed.

Thus, in the sheet feeding device 1, the sheet P is separated one by one and fed using the feed roller 15. Then, the sheet P is drawn from the nip between the pressing roller 16 and the separating member 17 without generating the multi feed.

First Embodiment

FIG. 5 is an explanatory view of a configuration of a sheet feeding device according to a first embodiment of the invention, FIG. 6 is an explanatory view of operation of a second sheet guide member of the sheet feeding device, and FIG. 7 is an explanatory view of a sheet feeding device according to a comparative example in which the second sheet guide member is eliminated. A sheet feeding device 1A of the comparative example has the same configuration as the first embodiment illustrated by FIGS. 1 and 2 except that the second sheet guide member 23 (FIG. 6) is eliminated. Therefore, the same component of FIG. 7 is designated by the same numeral of FIG. 6, and the overlapping description is neglected.

As illustrated in FIG. 5, in the sheet feeding device 1, the feed roller 15 is rotated and the top-most sheet P of the sheet stacking member 13 is fed while frictioned with the separating member 17. The sheet P fed by the feed roller 15 is separated one by one by the separating member 17 which is pressed against the feed roller 15 by the pressing spring 18. The surface friction coefficient, contact angle, and shape of the separating member 17 are adjusted such that only one top-most sheet P is conveyed in each feed operation.

The fed sheet P is guided to the first sheet guide member 22 to bend the course of the sheet P upward, and the sheet P is transferred to the pair of conveying rollers 21. The pair of conveying rollers 21 conveys the transferred sheet P while nipping the sheet P therebetween. At this point, the feed roller 15 is rotated once to stop the sheet feeding operation, and the cut-out portion of the feed roller 15 faces the separating member 17. Therefore, the sheet P is nipped between the pressing roller 16 and the separating member 17.

The pressing roller 16 is driven according to the sheet P drawn by the pair of conveying rollers 21. Similarly to the feed roller 15, the pressing roller 16 continuously presses the sheet P against the separating member 17, the second sheet multi-fed along with the first sheet P is blocked by the separating member 17.

As illustrated in FIG. 6, the pair of conveying rollers 21 is provided toward the side of the pressing roller 16 (the side on which the pressing roller 16 is disposed in relation to a tangent line A) from the tangent line A of the pressing roller 16 in the pressure-contact portion (nip portion) between the pressing roller 16 and the separating member 17.

The first sheet guide member 22 is provided between the feed roller 15 and the pair of conveying rollers 21, and the first sheet guide member 22 guides the sheet (P), fed to the feed roller 15, on the side of the separating member 17.

The second sheet guide member 23 is provided between the feed roller 15 and the pair of conveying rollers 21, and the second sheet guide member 23 guides the sheet (P), fed to the feed roller 15, on the side of the pressing roller 16.

A projection 23 a is formed in the second sheet guide member 23, and the projection 23 a is disposed on the tangent line A or at the position where the projection 23 a is projected toward the side of the separating member 17 from the tangent line A (the side on which the separating member 17 is disposed in relation to a tangent line A). The projection 23 a ensures a gap with the first sheet guide member 22 to form a sheet conveying passage.

The sheet (P) fed to the feed roller 15 is fed to the pair of conveying rollers 21 through a space between the first sheet guide member 22 and the second sheet guide member 23. The pressing roller 16 pressure-contacts the separating member 17 to prevent the multi feed of the sheet (P) after the sheet feeding operation is performed by the feed roller 15. Then, the sheet (P) is conveyed to the downstream by the pair of conveying rollers 21 so as to be drawn while nipped between the separating member 17 and the pressing roller 16.

As illustrated in FIG. 7, in the sheet feeding device 1A of the comparative example, because the pair of conveying rollers 21 is located on the side of the pressing roller 16 in relation to the tangent line A, the direction in which the sheet (P) is drawn becomes the direction in which the sheet (P) is wound around the pressing roller 16. In the comparative example, because the second sheet guide member 23 (FIG. 6) is eliminated, when the pair of conveying rollers 21 conveys the sheet (P), a tension F1 in a direction of a coupling line B1 toward the pair of conveying rollers 21 is applied to the sheet (P). The coupling line B1 is a line coupling the abutment portion between the pressing roller 16 and the separating member 17 and a point at which the sheet (P) contacts the conveying roller 19. The tension F1 in the direction of the coupling line B1 can be divided into a force Ft1 in a direction of the tangent line A and a force Fn1 applied to the pressing roller 16 toward a center 16 a.

Accordingly, the sheet (P) is drawn from the nip between the separating member 17 and the pressing roller 16 while generating a force pressing the pressing roller 16 toward the center 16 a. Therefore, the pressing roller 16 is vibrated to generate the noise according to the fluctuation in tension of the sheet (P).

However, in the first embodiment, as illustrated in FIG. 6, the projection 23 a of the second sheet guide member 23 is projected toward the side of the separating member 17 from tangent line A, and the gap is ensured between the projection 23 a and the first sheet guide member 22. Therefore, the direction in which the sheet (P) is drawn becomes a direction of a coupling line B2, when the pair of conveying rollers 21 conveys the sheet (P) toward the downstream side to draw the sheet (P) from the nip between the pressing roller 16 and the separating member 17. The coupling line B2 is a line drawn from the pressure-contact portion between the pressing roller 16 and the separating member 17 to the projection 23 a of the second sheet guide member 23.

When the pair of conveying rollers 21 draws the sheet (P), a tension F2 in the direction of the coupling line B2 is applied to the sheet (P), and the tension F2 is divided into a force Ft2 in the direction of the tangent line A and a force Fn2 in a direction of the normal line C. Because the force Fn2 in the direction of the normal line C is separated from the center 16 a of the pressing roller 16, the pressing roller 16 is not pressed toward the center 16 a by the sheet (P) or separating member 17 when the pair of conveying rollers 21 draws the sheet (P). Accordingly, the vibration and noise generated by the fluctuation of the force Fn1 with which the pressing roller 16 is pressed toward the center 16 a can be reduced when the sheet (P) shown in FIG. 7 is drawn.

In the first embodiment, the vibration and noise can be suppressed on the downstream side distant from the structure separating the sheet irrespective of the addition of the member around the separating member or the change in pressure-contact state. Therefore, the change in configuration does not have an influence on the separation feed performance. The generation of the force in the direction in which the separating member is pressed against the pressing roller by the drawing of the sheet, which is of the noise factor, is eliminated to reduce the noise with no influence on the separation feed performance.

In the first embodiment, a part of the second sheet guide member is projected on the tangent line drawn to the abutment surface of the pressing roller in the abutment portion (nip portion) between the pressing roller and the separating member or toward the separating member side from the tangent line. The part of the second sheet guide member is provided between the first sheet guide member and the second sheet guide member.

Therefore, the sheet drawing direction becomes the tangent line direction or the direction located on the separating member side in relation to the tangent line (direction inclined from the tangent line toward the side on which the separating member is disposed based on the abutment portion), and the force with which the separating member is pressed against the pressing roller by the drawing the sheet is eliminated or reduced, so that the generation of the noise can be reduced when the pair of conveying rollers conveys the sheet while the sheet is nipped between the separating member and the pressing roller. Even if the pressing force of the pressing roller is decreased, the sheet continuously presses the separating member with the tension. Therefore, the sheet intruding between the sheet and the separating member is blocked to avoid the multi feed of the sheet by the separating member.

Second Embodiment

FIG. 8 is an explanatory view of a configuration of a sheet feeding device according to a second embodiment of the invention, and FIG. 9 is an explanatory view of operation of a second sheet guide member of the sheet feeding device. A sheet feeding device 1B of the second embodiment has the same configuration as the first embodiment except that the second sheet guide member 23 is replaced with a second sheet guide member 24. Therefore, the same component of FIGS. 8 and 9 is designated by the same numeral of FIG. 6, and the overlapping description is not presented.

As illustrated in FIG. 8, similarly to the first embodiment, the sheet feeding device 1B of the second embodiment includes the sheet stacking member 13, the feed roller 15, the pressing roller 16, the separating member 17, the pressing spring 18, and the pair of conveying rollers 21. In the pressing roller 16, the feed roller 15 is provided integrally or detachably. The pressing roller 16 abuts on the separating member 17 to prevent the multi feed of the sheet P after the feed roller 15 is operated. The separating member 17 is swingably supported by the swing support 17 a located on the upstream side in the conveying direction of the separating member 17.

The sheet P placed on the sheet stacking member 13 is fed by the feed roller 15 and separated one by one by the separating member 17. The separating member 17 is pressed against the feed roller 15 by the pressing spring 18.

The surface friction coefficient, contact angle, and shape of the separating member 17 are adjusted such that only one top-most sheet P is conveyed in each feed operation.

After feeding the sheet P, the separating member 17 is pressed against the pressing roller 16 to nip the sheet P therebetween. The sheet P is fed to the pair of conveying rollers 21 while guided by the first sheet guide member 22 and the second sheet guide member 24. Then, the sheet P is conveyed toward the downstream side by the pair of conveying rollers 21 so as to be drawn while nipped between the separating member 17 and the pressing roller 16.

As illustrated in FIG. 8, the pair of conveying rollers 21 is provided on the side of the pressing roller 16 from the tangent line A of the pressing roller 16 in the abutment portion between the pressing roller 16 and the separating member 17 (the side on which the separating member 17 is disposed in relation to a tangent line A).

The first sheet guide member 22 is provided between the feed roller 15 and the pair of conveying rollers 21, and the first sheet guide member 22 guides the sheet (P), fed to the feed roller 15, on the side of the separating member 17.

A second sheet guide member 24 is provided between the feed roller 15 and the pair of conveying rollers 21, and the second sheet guide member 24 guides the sheet (P), sent to the feed roller 15, on the side of the pressing roller 16.

A projection 24 a is formed in the second sheet guide member 24, and the projection 24 a is disposed on the tangent line A or at the position where the projection 24 a is projected toward the side of the separating member 17 from the tangent line A. The projection 24 a ensures a gap with the first sheet guide member 22.

The pair of conveying rollers 21 which is of an example of the sheet conveying unit and the second sheet guide member 24 which is of an example of the second guide member are exchangeably assembled integral with each other while a positional relationship is fixed between the pair of conveying rollers 21 and the second sheet guide member 24. The second sheet guide member 24 retains the pair of conveying rollers 21.

Because the pair of conveying rollers 21 is provided on the side of the pressing roller 16 in relation to the tangent line A, the direction in which the sheet (P) is drawn becomes the direction in which the sheet (P) is wound around the pressing roller 16 when the second sheet guide member 24 is eliminated (see FIG. 7). Therefore, when the pair of conveying rollers 21 conveys the sheet (P), the sheet (P) is drawn while the force pushing up the pressing roller 16 is generated. At this point, when the frictional state with the separating member 17 fluctuates to generate the fluctuation in tension F3 of the sheet (P), the vibration is possibly generated in the direction in which the pressing roller 16 is pushed up to generate the noise.

However, in the second embodiment, the projection 24 a formed in the second sheet guide member 24 is projected toward the side of the separating member 17 from the tangent line A (the side on which the separating member 17 is disposed in relation to a tangent line A), and the gap is ensured with the first sheet guide member 22. Therefore, the direction in which the sheet (P) is drawn becomes a direction of a coupling line B3, when the pair of conveying rollers 21 conveys the sheet (P) toward the downstream side so as to draw the sheet (P) from the nip between the pressing roller 16 and the separating member 17. The coupling line B3 is a line drawn from the pressure-contact portion (nip portion) between the pressing roller 16 and the separating member 17 to the projection 24 a of the second sheet guide member 24.

When the pair of conveying rollers 21 draws the sheet (P), a tension F3 in the direction of the coupling line B3 is applied to the sheet (P), and the tension F3 is divided into a force Ft3 in the direction of the tangent line A and a force Fn3 in a direction of the normal line C. Because the force Fn3 in the direction of the normal line C is separated from the center 16 a of the pressing roller 16, the pressing roller 16 is not pressed toward the center 16 a by the drawing force of the sheet (P) when the pair of conveying rollers 21 draws the sheet (P). Accordingly, the vibration and noise are reduced.

In the case where the attaching position of the second sheet guide member 24 to the pair of conveying rollers 21 varies, the sheet (P) cannot be guided to the desired position, the direction in which the sheet (P) is drawn does not become the direction of the tangent line A or the side of the separating member 17 in relation to the tangent line A, and possibly the generation of the vibration or noise cannot sufficiently be reduced.

However, in the second embodiment, as described above, the second sheet guide member 24 retains the pair of conveying rollers 21, and the positional accuracy of the second sheet guide member 24 can be kept at a high level with respect to the pair of conveying rollers 21. Therefore, the sheet P can be drawn more correctly in the direction of the tangent line A or onto the side of the separating member 17 in relation to the tangent line A, and the generation of the vibration or noise can be reduced more surely.

In the second embodiment, the second sheet guide member retains the pair of conveying rollers, and the positional accuracy of the second sheet guide member 24 can be kept at a high level with respect to the pair of conveying rollers 21. Therefore, the sheet P can be drawn more correctly in the direction of the tangent line or the direction located on the side of the separating member in relation to the tangent line A (direction inclined from the tangent line toward the side on which the separating member is disposed based on the abutment portion), and the generation of the noise can be reduced more surely.

Third Embodiment

FIG. 10 is an explanatory view of a configuration of a sheet feeding device according to a third embodiment of the invention, and FIG. 11 is an explanatory view of operation of a second sheet guide member of the sheet feeding device. A sheet feeding device 1C of the third embodiment has the same configuration as the second embodiment except that the second sheet guide member 24 is replaced with a second sheet guide member 25. Therefore, the same component of FIGS. 10 and 11 is designated by the same numeral of FIGS. 8 and 9, and the overlapping description is not presented.

As illustrated in FIG. 10, similarly to the second embodiment, the sheet feeding device 1C of the third embodiment includes the sheet stacking member 13, the feed roller 15, the pressing roller 16, the separating member 17, the pressing spring 18, and the pair of conveying rollers 21. In the pressing roller 16, the feed roller 15 is provided integrally or detachably. The pressing roller 16 abuts on the separating member 17 to prevent the multi feed of the sheet P after the feed roller 15 is operated. The separating member 17 is swingably supported by the swing support 17 a located on the upstream side in the conveying direction of the separating member 17.

The sheet P placed on the sheet stacking member 13 is fed by the feed roller 15 and separated one by one by the separating member 17. The separating member 17 is pressed against the feed roller 15 by the pressing spring 18.

The surface friction coefficient, contact angle, and shape of the separating member 17 are adjusted such that only one top-most sheet P is conveyed in each feed operation.

After feeding the sheet P, the separating member 17 is pressed against the pressing roller 16 to nip the sheet P therebetween. The sheet P is fed to the pair of conveying rollers 21 while guided by the first sheet guide member 22 and the second sheet guide member 25. Then, the sheet P is conveyed toward the downstream side by the pair of conveying rollers 21 so as to be drawn while nipped between the separating member 17 and the pressing roller 16.

As illustrated in FIG. 11, the pair of conveying rollers 21 is provided on the side of the pressing roller 16 from the tangent line A of the pressing roller 16 in the abutment portion between the pressing roller 16 and the separating member 17 (the side on which the separating member 17 is disposed in relation to a tangent line A). The first sheet guide member 22 is provided between the feed roller 15 and the pair of conveying rollers 21, and the first sheet guide member 22 guides the sheet (P), fed to the feed roller 15, on the side of the separating member 17.

The second sheet guide member 25 is provided between the feed roller 15 and the pair of conveying rollers 21, and the second sheet guide member 25 guides the sheet (P), fed to the feed roller 15, on the side of the pressing roller 16.

A projection 25 a is formed in the second sheet guide member 25, and the projection 25 a is disposed on the tangent line A or at the position where the projection 25 a is projected toward the side of the separating member 17 from the tangent line A (the side on which the separating member 17 is disposed in relation to a tangent line A). The projection 25 a ensures a gap with the first sheet guide member 22.

The pair of conveying rollers 21 which is of an example of the sheet conveying unit and the second sheet guide member 25 which is of an example of the second guide member are exchangeably assembled integral with each other while a positional relationship is fixed between the pair of conveying rollers 21 and the second sheet guide member 24. The second sheet guide member 25 retains the pair of conveying rollers 21.

A projection 25 a which is of an example of the second guide member is rotatably supported by the second sheet guide member 25, and the projection 25 a is a rotating body which is driven according to the sheet (P) drawn from the nip between the separating member 17 and the pressing roller 16. The projection 25 a of the second sheet guide member 25 is disposed while projected toward the separating member 17 from to the tangent line A, and the projection 25 a is a roller which is rotatable with respect to the sheet (P).

The sheet (P) is conveyed to the downstream side by the pair of conveying rollers 21 so as to be drawn while nipped between the separating member 17 and the pressing roller 16. At this point, because the pair of conveying rollers 21 is provided on the side of the pressing roller 16 in relation to the tangent line A, the direction in which the sheet (P) is drawn becomes the direction in which the sheet (P) is wound around the pressing roller 16 when the second sheet guide member 25 is eliminated (see FIG. 7). Therefore, when the pair of conveying rollers 21 conveys the sheet (P), because the sheet (P) is drawn while the force pushing up the pressing roller 16 is generated, the pressing roller 16 is vibrated to generate the noise.

However, in the third embodiment, the projection 25 a is projected from the tangent line A to ward the side of the separating member 17 while the gap with the first sheet guide member 22 is ensured, so that the direction in which the sheet (P) is drawn becomes the direction of a coupling line B4. The coupling line B4 is a line drawn from the abutment portion between the pressing roller 16 and the separating member 17 to the projection 25 a of the second sheet guide member 25.

Therefore, the sheet (P) is conveyed onto the downstream side by the pair of conveying rollers 21 so as to be drawn in the coupling line B4 while nipped between the pressing roller 16 and the separating member 17. At this point, a tension F4 applied to the sheet (P) in the direction of the coupling line B4 is divided into a force Ft4 in the direction of the tangent line A and a force Fn4 in the direction of the normal line C. Because the force Fn4 in the direction of the normal line C is separated from the center 16 a of the pressing roller 16, the pressing roller 16 is not pressed toward the center 16 a by the sheet (P) drawn from the nip between the separating member 17 and the pressing roller 16. Accordingly, the vibration and noise generated by the fluctuation of the force F4 can be reduced.

The second sheet guide member 25 retains the pair of conveying rollers 21, and the positional accuracy of the second sheet guide member 25 can be kept at a high level even after the pair of conveying rollers 21 is replaced. Therefore, the sheet P can be drawn more correctly in the direction of the tangent line or the direction located on the side of the separating member 17 in relation to the tangent line A, and the generation of the noise can be reduced more surely.

The projection 25 a of the second sheet guide member 25 is formed by a rotatable roller, and the projection 25 a is driven by the sheet (P). Therefore, the sheet (P) can be drawn with lesser drawing resistance compared with the second embodiment. Accordingly, the fluctuation in tension F4 of the sheet (P) can further be decreased to reduce the generation of the vibration and noise in the pressing roller 16.

That is, when the pair of conveying rollers 21 conveys the sheet (P) onto the downward side, the sheet (P) is slid while brought into pressure-contact with the second sheet guide member 25. Therefore, the rubbing noise is possibly generated between the sheet (P) and the second sheet guide member 25, or the friction between the sheet (P) and the second sheet guide member 25 possibly becomes the conveying resistance to generate variations in conveyance.

However, in the third embodiment, because the projection 25 a of the second sheet guide member 25 is formed by the roller which is rotatable with respect to the sheet (P), the rolling contact is generated between the sheet (P) and second sheet guide member 25 when the pair of conveying rollers 21 conveys the sheet (P). Therefore, the generation of the rubbing noise can be reduced while the variations in conveyance caused by the conveying resistance are also reduced. Accordingly, the fluctuation in speed of the sheet is decreased in the image forming portion G of FIG. 1 to improve the image quality.

In the third embodiment, because the projection of the second sheet guide member is formed by the roller which is rotatable with respect to the sheet, the contact between the sheet and second sheet guide member can be changed from the sliding contact to the rolling contact when the pair of conveying rollers conveys the sheet. Accordingly, the generation of the rubbing noise can be reduced while the variations in conveyance caused by the conveying resistance are also reduced.

The invention can be implemented in another embodiment in which a part of or the whole of the configuration of the embodiments is replaced by an alternative configuration as long as the sheet is drawn from the nip between the pressing member and the separating member while the course of the sheet is bent toward the sheet feed member side.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2007-52106, filed Mar. 1, 2007, which is hereby incorporated by reference herein in its entirety. 

1. A sheet feeding device comprising: a sheet feed member which feeds a sheet; a separating member which separates the sheet one by one between the sheet feed member and the separating member; a first guide member which guides the sheet fed by the sheet feed member while bending the sheet toward a sheet feed member side; a sheet conveying unit which conveys the sheet guided by the first guide member while nipping the sheet; and a second guide member which orientates a course of the sheet toward a sheet conveying unit side, wherein the second guide member contacts a surface on the sheet feed member side of the sheet drawn from between the sheet feed member and the separating member, on a tangent line of the sheet feed member at a position where the sheet feed member contacts the separating member, or at a position located on a separating member side in relation to the tangent line.
 2. The sheet feeding device according to claim 1, wherein the sheet feed member includes a rotating body which is rotatably supported and driven according to the sheet drawn by the sheet conveying unit, and the tangent line is defined by a tangent line of the rotating body at a position where the rotating body pressure-contacts the separating member.
 3. The sheet feeding device according to claim 2, wherein the second guide member includes a rotating body which is rotatably supported and driven according to the drawn sheet.
 4. The sheet feeding device according to claim 2, wherein the sheet conveying unit and the second guide member are exchangeably assembled integral with each other while a positional relationship is fixed between the sheet conveying unit and the second guide member.
 5. An image forming apparatus comprising: the sheet feeding device as in any one of claims 1 to 4; and an image forming unit which forms an image in a sheet fed from the sheet feeding device. 